In the production of thermal ink-jet pens for use in ink-jet printers, a printhead is bonded to the body of the pen. The printhead includes, inter alia, a plenum chamber for conducting ink to a plurality of firing chambers and a nozzle plate with nozzles, one for each firing chamber. Each firing chamber includes a resistor for propelling a droplet of ink through the nozzle toward an ink-receptive surface, such as paper.
The body of the pen serves as a reservoir for the ink and is fluidically connected to the plenum chamber in the printhead.
During assembly of the printhead on the pen body, an adhesive is used to bond the two together. The adhesive also "fixtures" the printhead to the pen body such that its location relative to the pen body is known and does not shift during processing or use. Further, the adhesive provides an additional function in serving as a fluid gasket against leakage of ink.
However, the printhead and the pen body have dissimilar coefficients of thermal expansion, since the surface of the printhead bonded to the pen body is silicon and the pen body is either a plastic such as a modified phenylene oxide or stainless steel. Thus, the adhesive must accommodate both the dissimilar expansions and contractions of the printhead and the pen body and be impermeable to attack by the ink, which is commonly a vehicle of water and at least one glycol and/or glycol ether plus dye, plus other substances, such as pH modifiers, biocides, etc. The present adhesive exhibits porosity (unpredictably), which leads to leakage and failure of the gasketing function.